Cooling method for liquefying a feed gas

ABSTRACT

The present invention pertains to a cooling method for liquefying a feed gas, comprising the steps of providing a cooling cycle with a refrigerant stream; dividing the refrigerant stream into a first partial stream and a second partial stream; expanding the first partial stream in a first expansion device; and transferring cooling energy from the expanded first partial stream to a feed gas stream to be cooled, particularly comprising hydrogen and/or helium. Further the method comprises the steps of guiding the expanded first partial stream to a suction inlet of an ejector; and guiding the second partial stream to a propellant inlet of the ejector such that, upon expanding the second partial stream in the ejector, the expanded first partial stream is compressed and merged with the expanded second partial stream.

TECHNICAL FIELD

The invention relates to a cooling method and a cooling system forliquefying a feed gas, for example hydrogen.

TECHNOLOGICAL BACKGROUND

In general, industrial hydrogen liquefaction plants are known, forexample from EP 3 163 236 A1, in which a hydrogen gas stream is cooledby means of a plurality of closed-loop cooling cycles to a temperaturebelow a condensation point of hydrogen so as to provide a liquidhydrogen stream.

The known industrial hydrogen liquefaction plants typically comprise ahydrogen cooling and liquefaction unit, to which a hydrogen feed gasstream to be cooled is supplied with a typical feed pressure between 15bar and 30 bar. The hydrogen feed gas stream is usually produced outsidethe battery-limit of the plant, for example by means of a methane steamreformer or an electrolyzer.

Upon flowing through the hydrogen cooling and liquefaction unit, thehydrogen gas stream is cooled to a temperature below its condensationpoint and thereby liquefied prior to being discharged into a storagetank. In order to provide cooling energy for cooling and liquefaction ofthe hydrogen gas stream, the hydrogen cooling and liquefaction unit isthermally coupled to several cooling cycles by means of a plurality ofheat exchangers.

Specifically, in a precooling cycle, the evaporation of a liquidnitrogen stream at typically 78 K is used, which is the nitrogensaturation temperature for an ambient pressure of 1.1 bar, to precoolthe hydrogen feed stream from ambient temperature to about 80 K. This isachieved by guiding the nitrogen stream of the precooling cycle and thehydrogen feed gas stream through a heat exchanger so as to transfercooling energy. Thereafter, the hydrogen feed is typically conductedthrough a purifier to remove residual impurities, mainly nitrogen, in anadsorber vessel. After the purification at 80 K, the hydrogen feed isallowed to pass through additional heat exchanger passages filled withcatalyst, typically hydrous ferric oxide, for an ortho to para hydrogenconversion. In case of deuterium liquefaction, the para “isomer” isconverted to ortho. The feed gas stream is then again cooled down toabout 80 K by the means of liquid nitrogen of the precooling cycle.

A final cooling and liquefaction of the hydrogen feed, from about 80 Kto the state of saturated or subcooled liquid, is provided by means of aclosed main cooling cycle, for example a Claude loop, with typically oneor more cooling strings with turbines expanding the gas from a highpressure to medium pressure to provide refrigeration at differenttemperature levels. Specifically, the number of cooling strings maydepend on the output capacity of the plant. As a result, a mediumpressure stream is generated. As soon as the expansion of hydrogen in anisenthalpic expansion will result in a significant temperature decrease,the application of ejectors or a Joule Thomson valve becomes meaningful.The last or the coldest high-pressure refrigeration stream is expandedin a Joule-Thomson valve to a low pressure and lowest temperature level.In this way, a two-phase gas liquid stream is generated to providecooling energy capable of cooling the hydrogen gas stream below thecondensation point. For heat recovery purposes, the high-pressure streamis run counter currently against the medium and low-pressure stream inseries of a plurality of heat exchanger, e.g. up to ten or more heatexchangers depending on the plant size and number of turbines.

For recirculating the medium and low-pressure stream, the main coolingcycle typically comprises a low-pressure compressor which collects andcompresses the low-pressure stream to medium pressure. Further, a mediumpressure compressor is provided which collects the total medium pressurestream and compresses it to high pressure before being reintroduced intothe closed cycle. Usually, these compressors are mechanically orelectrically driven.

However, the use of mechanically or electrically driven compressors forraising the pressure level of the low-pressure stream to a mediumpressure level has an impact of the operational and capital expendituresof such industrial hydrogen liquefaction plants.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an optimized coolingmethod used for liquefying a feed gas, particularly in an industrialhydrogen liquefaction plant, which can be cost-efficiently realized.Further, it is an object of the present invention to provide acorresponding cooling system.

These objects are addressed by a cooling method having the features ofclaim 1 and a cooling system having the features of claim 9.

A cooling method is provided for liquefying a feed gas. The coolingmethod comprises the steps of providing a cooling cycle with arefrigerant stream; dividing the refrigerant stream into a first partialstream and a second partial stream; expanding the first partial streamin a first expansion device and transferring cooling energy from theexpanded first partial stream to a feed gas stream to be cooled. Thecooling method is characterized by comprising the further steps ofguiding the expanded first partial stream to a suction inlet of anejector and guiding the second partial stream to a propellant inlet ofthe ejector such that, upon expanding the second partial stream in theejector, the expanded first partial stream is compressed and merged withthe expanded second partial stream.

The feed gas stream to be cooled may comprise one or more cryogenicgases. Specifically, the feed gas stream to be cooled may comprisehydrogen. Alternatively, or additionally, the feed gas stream maycomprise helium. Further, the feed gas stream may comprise Oxygen and/orother cryogenic gases.

The refrigerant stream may also comprise one or more cryogenic gases.Specifically, the refrigerant stream may comprise hydrogen or helium orneon. Alternatively, or additionally, the refrigerant stream maycomprise a mixture of gases, i.e. a mixture of the previously mentionedgases, e.g. a mixture of neon and helium.

The proposed method may be used in in an industrial cryogenic gasliquefaction plant, i.e. a hydrogen liquefaction plant. Further, theproposed method may be used in cooling cycles, i.e. precooling cycles,e.g. in such a gas liquefaction plant.

According to the present disclosure, the term “ejector” refers to apumping device, i.e. a fluid jet ejector, in which a pumping effect isgenerated due to an induced momentum transfer of a motive or propellantmedium to a suction medium, thereby accelerating and/or compressing thesuction medium. In other words, impulses are exchanged between thepropellant medium, i.e. a high velocity gas jet, and the suction medium.Preferably, the ejector, i.e. the fluid jet ejector, comprises thepropellant inlet for receiving a pressurized propellant fluid that issupplied to a nozzle, i.e. a lava! nozzle, communicating to a suctionchamber of the ejector which is configured to generate a suctionpressure therein which is lower than an ejector discharge pressure. Theejector further comprises the suction inlet which opens into the suctionchamber and is configured to supply a suction fluid into the suctionchamber, wherein the suction fluid has a pressure lower than a pressureof the propellant fluid supplied to the propellant inlet. The suctionchamber communicates to a fluid outlet of the ejector via aconvergent-divergent diffuser.

In operation of the ejector, the pressurized propellant fluid enters thepropellant inlet of the ejector and is then accelerated to a highvelocity through the nozzle which discharges a high velocity jet streamof the fluid through the suction chamber into the convergent-divergentdiffuser. Acceleration of the pressurized propellant fluid through thenozzle into the suction chamber creates a reduced pressure in thechamber which feeds a suction fluid from the suction inlet into thesuction chamber. The suction fluid thus entering the suction chamber isentrained by and drawn into the convergent-divergent diffuser with thehigh velocity fluid stream. The combined fluid is subjected toacceleration and compression as it passes through a convergent inletportion of the diffuser and, thereafter, deceleration and expansion asit passes through the divergent outlet portion of the diffuser. Independence on the geometrical configuration of the ejector, inparticular of the convergent-divergent diffuser, a velocity and pressureof the combined fluid output by the ejector via the output line can beset.

Preferably, the second partial stream constitutes the pressurizedpropellant fluid supplied to the propellant inlet and the expanded firstpartial stream constitutes the suction fluid supplied to the suctioninlet of the ejector. In this way, upon flowing through the ejector, anexpanded refrigerant stream may be provided by merging the compressedfirst partial stream with the expanded second partial stream in theejector. Preferably, the ejector is designed and configured such thatthe expanded refrigerant stream output by the ejector has a mediumpressure that is higher than a low pressure prevailing in the expandedfirst partial stream and that is lower than an intermediate or highpressure prevailing in the second partial stream or the refrigerantstream.

Generally, in the cooling cycle, the expanded first partial stream isprovided with a sufficient low temperature so as to provide sufficientcooling energy for liquefying the feed gas stream. Therefore, the firstpartial stream is subjected to a high pressure drop from high pressureto low pressure to sufficiently decrease the temperature thereof. Forreintroducing the expanded first partial stream into the cooling cycle,i.e. the refrigerant stream, it is subjected to a compression.

According to the present invention, the compression of the expandedfirst partial stream, i.e. from low to medium pressure, is performed bymeans of the ejector. Compared to conventionally used compressiondevices for compressing the low-pressure refrigerant stream to a mediumand high pressure, the ejector is characterized by a simple and reliabledesign which is free of movable parts. Specifically, in the knownmethods and systems for liquefying hydrogen, mechanically orelectrically driven compressors are used, e.g. rotary or reciprocatingdriven compressors. Such compressors, however, are expensive and requirecostly and time-consuming maintenance. This applies in particular whenhydrogen as a refrigerant medium in the cooling cycle is used which mayrequire an oil free operation of the corresponding compressors. Further,such compressors are typically operated at ambient temperatureconditions, i.e. outside a so-called cold box of gas liquefactionplants, thereby requiring additional passage-lines, such as return linesor passage-lines in the heat exchangers.

Thus, by using an ejector for compressing the low pressure expandedfirst partial stream, the present invention provides a cost-optimizedcooling method. Specifically, as the ejector is less expansive topurchase and maintain, the present invention contributes to solving thetrade-off between operational and capital expenditures when designingindustrial hydrogen liquefaction plants.

Specifically, the proposed cooling method may be used for liquefyinghydrogen in an industrial hydrogen liquefaction plant. Such industrialhydrogen liquefaction plant preferably comprises a hydrogen cooling andliquefaction unit, to which a hydrogen feed gas stream is supplied witha typical feed pressure between 15 bar and 30 bar. Upon flowing throughthe hydrogen cooling and liquefaction unit, the hydrogen feed gas streamis preferably cooled and thereby liquefied so as to generate a liquidproduct stream. Thereafter, the liquid product stream may be guidedtowards a storage tank for storing the liquefied hydrogen at a desiredstorage pressure, e.g. 1.1 bar, and a desired storage temperature, e.g.20 K.

Further, the industrial hydrogen liquefaction plant preferably comprisesa cooling system having the cooling cycle, in which the proposed coolingmethod is performed and which is thermally coupled to the hydrogencooling and liquefaction unit for providing cooling energy forliquefying the feed gas stream flowing through the hydrogen cooling andliquefaction unit. This thermal coupling is preferably realized by meansof at least a first heat exchanger configured to transfer cooling energyfrom the expanded first partial stream circulating through the coolingcycle to the feed gas stream to be cooled, which flows through thehydrogen cooling and liquefaction unit. Specifically, by transferringcooling energy from the expanded first partial stream to the feed gasstream to be cooled, particularly by means of the first heat exchanger,the cooling method is intended to cool the feed gas stream to atemperature below a critical temperature of hydrogen so as to providethe liquid product stream comprising hydrogen.

The cooling cycle for generating cooling energy for the hydrogen coolingand liquefaction unit is preferably provided in form of the coolingcycle having the refrigerant stream comprising hydrogen. The coolingcycle is preferably provided as a closed cooling cycle, in which therefrigerant circulates. For providing the closed cooling cycle, theexpanded refrigerant stream, which is provided by merging the compressedfirst partial stream with the expanded second partial stream in theejector, may be guided through a compressor unit so as to compress theexpanded refrigerant stream to a high pressure level, thereby providingthe refrigerant stream. The compressor unit may comprise one or morecompressor devices, e.g. piston compressors, for compressing theexpanded refrigerant stream depending on the intended pressure change.For example, the compressor unit may comprise at least one, preferablytwo piston compressors. However, the proposed method is not limitedthereto. Rather, the cooling cycle may also be provided as an opencooling cycle.

The method may further comprise a step of guiding the expandedrefrigerant stream and the first partial stream such that heat istransferred between the expanded refrigerant stream and the firstpartial stream. This may be achieved by a second heat exchangerconfigured to transfer cooling energy from the expanded refrigerantstream to the first partial stream. In a further development, theexpanded refrigerant stream and the first partial stream may be guidedsuch that cooling energy is further transferred from the expandedrefrigerant stream and/or the first partial stream to the feed gasstream flowing through the hydrogen cooling and liquefaction unit.Specifically, this may be realized by thermally coupling the feed gasstream to the expanded refrigerant stream and/or the first partialstream particularly by means of the second heat exchanger. In otherwords, the second heat exchanger may be provided such that each of thefirst partial stream, the expanded refrigerant stream and the feed gasstream flow therethrough. In this way, the cooling method providesrefrigeration at different temperature levels, thereby improving anoverall efficiency of the cooling method as a successive cooling of thefeed gas stream may be provided.

In the further development, the second partial stream may be partiallyexpanded and thereby cooled in a second expansion device prior to beingguided or supplied to the ejector, i.e. to its propellant inlet. In thisway, an expanded second partial stream may be generated having anintermediate pressure that is higher than the medium pressure.Specifically, the second expansion device may comprise aJoule-Thomson-valve and/or an expansion turbine. The expansion turbinemay be capable or designed to generate mechanical or electrical energyupon expansion of the second partial stream, e.g. by means of a brakewheel, in order to provide energy recovery. For example, the expansionturbine may be designed to drive the compressor unit for compressing theexpanded refrigerant stream. To that end, the generated electricalenergy may be supplied to a power grid or may be used elsewhere.Further, for control purposes, a bypass line may be provided throughwhich at least a part of the second partial stream is guided, and whichis configured for bypassing the second expansion device and guiding thesecond partial stream flowing therethrough into the ejector, i.e.directly into the ejector.

Additionally, or alternatively, the refrigerant stream may be furtherdivided into at least one third partial stream. Specifically, therefrigerant stream may be divided into the first, the second and the atleast one third partial stream after passing the different heatexchanger having different temperature levels, respectively. In otherwords, the refrigerant forming the respective partial stream is branchedoff from the refrigerant stream at different positions, at which therefrigerant has different temperatures. Accordingly, the first partialstream, the second partial stream and the at least one third partialstream, respectively, comprise different temperature levels. In thisway, multi-level refrigeration at different temperature levels can beprovided, thereby further contributing to an improved overall efficiencyof the cooling method. This may be realized by the method furthercomprising the steps of expanding the at least one third partial streamin at least one third expansion device, and guiding the at least oneexpanded third partial stream, the first partial stream and the secondpartial stream such that heat is transferred, particularly by means ofat least one third heat exchanger, between the at least one expandedthird partial stream, the first partial stream and the second partialstream.

In a further development, the first partial stream, the second partialstream and the at least one expanded third partial stream may be guidedsuch that cooling energy is further transferred from the first partialstream, the second partial stream and/or the at least one expanded thirdpartial stream to the feed gas stream flowing through the hydrogencooling and liquefaction unit. Specifically, this may be realized bythermally coupling the feed gas stream to the first partial stream, thesecond partial stream and/or the at least one expanded third partialstream particularly by means of the at least one third heat exchanger.In other words, the at least one third heat exchanger may be providedsuch that each of the at least one expanded third partial stream, thefirst partial stream and the feed gas stream flow therethrough.Specifically, the at least one expanded third partial stream may be feedto the expanded refrigerant stream, e.g. downstream of the at least onethird heat exchanger. According to the present disclosure, the terms“downstream” and “upstream” refer to a flow direction of the respectivestream through the passages of the cooling cycle or hydrogen cooling andliquefaction unit.

Further, the at least one third expansion device may be provided in formof at least one further expansion turbine. According to the abovedescribed expansion turbine, also the at least one further expansionturbine may be capable or designed to generate mechanical or electricalenergy upon expansion of the at least one third partial stream, e.g. bymeans of a brake wheel, in order to provide energy recovery.

Additionally, or alternatively, the expanded first partial stream isguided into a gas liquid separator arranged downstream of the firstexpansion device and configured to store the refrigerant in a liquid andgaseous phase, wherein the expanded first partial stream in a liquidphase is guided from the separator to the suction inlet of the ejector.

In a further development, the cooling system of the industrial hydrogenliquefaction plant may further comprise a closed precooling cycleconfigured to precool the refrigerant stream and/or the feed gas stream.Accordingly, the cooling method may comprise a step of precooling therefrigerant stream by means of a closed precooling cycle having afurther refrigerant stream comprising or consisting of nitrogen, whereinin particular the further refrigerant stream is expanded in a fourthexpansion device prior to being supplied to a fourth heat exchanger fortransferring cooling energy to the refrigerant stream and particularlyto the feed gas stream.

Furthermore, a cooling system used for liquefying the feed gas stream isprovided, which may be used in the above described industrial hydrogenliquefaction plant. Specifically, the cooling system may be provided toperform the above described cooling method. Thus, the technical featurespreviously described in connection with the method may also apply to thecooling system. In other word these features are also disclosed inconnection with the cooling system.

The cooling system has a cooling circuit with the refrigerant streamcirculating through a refrigerant line. Specifically, the coolingcircuit further comprises an expansion device configured to expand afirst partial stream flowing through a first junction line whichbranches off from the refrigerant line and a heat exchanger fortransferring cooling energy from the expanded first partial stream tothe feed gas stream to be cooled. In other words, in the heat exchanger,heat is transferred from the feed gas stream to be cooled to theexpanded first partial stream. The cooling system is characterized inthat the cooling circuit further comprises an ejector having a suctioninlet connected to the first junction line for receiving the expandedfirst partial stream and a propellant inlet connected to a secondjunction line which branches off from the refrigerant line for receivinga second partial stream, wherein the ejector is configured to, uponexpanding the second partial stream in the ejector, compress theexpanded first partial stream and merge it with the expanded secondpartial stream.

As described above, the feed gas stream to be cooled may comprise one ormore cryogenic gases. Specifically, the feed gas stream to be cooled maycomprise hydrogen. Alternatively, or additionally, the feed gas streammay comprise helium. Further, the feed gas stream may comprise oxygenand or other cryogenic gases. Further, the refrigerant stream may alsocomprise one or more cryogenic gases. Specifically, the refrigerantstream may comprise hydrogen or helium or neon. Alternatively, oradditionally, the refrigerant stream may comprise a mixture of gases,i.e. a mixture of the previously mentioned gases, e.g. a mixture of neonand helium.

The heat exchanger may be configured to transfer cooling energy from theexpanded first partial stream to the feed gas stream to be cooled suchthat the feed gas stream is cooled to a temperature below its criticaltemperature so as to provide a liquid product stream. The cooling may beperformed in such a way that a two-phase region is reached byisenthalpic expansion. More specifically, the cooling may be performedin such a way that the feed gas stream, after isenthalpic expansion intothe product storage tank, may be provided in the form of a subcooled orat least saturated liquid. For example, in case the feed gas streamcomprises hydrogen, the feed gas stream may be cooled to a temperatureof at least 33 K. The temperature of 33 K may be the critical point ofthe feed gas stream comprising hydrogen. Thus, in order to have phaseseparation, the feed gas stream may be cooled to a temperature below 33K.

The cooling system may further comprise a compressor and/or ejector unitconfigured to compress an expanded refrigerant stream output by theejector and formed by merging the compressed first partial stream withthe expanded second partial stream so as to provide the refrigerantstream, and wherein the compressor and/or ejector unit takes bothstreams back to at least one compressor device, e.g. piston compressor,in case the cooling cycle is a closed cooling cycle.

A second heat exchanger may be provided which is configured to transferheat between the expanded refrigerant stream and the first partialstream and particularly the feed gas stream.

The cooling system may further comprise a second expansion device,particularly a Joule-Thomson-valve and/or an expansion turbine, arrangedupstream of the ejector. The second expansion device may be configuredto partially expand the second partial stream flowing through the secondjunction line. In a further development, the cooling system may compriseat least one third expansion device configured to expand at least onethird partial stream flowing through at least one third junction linewhich branches off from the refrigerant line at different temperaturelevels. In addition, at least one third heat exchanger may be providedfor transferring heat between the at least one expanded third partialstream and the first partial stream and particularly the feed gasstream. Further, at least one supply line may be arranged downstream ofthe at least one third heat exchanger for feeding the at least oneexpanded third partial stream to the expanded refrigerant stream.

Alternatively, or additionally, the cooling system may further comprisea gas liquid separator arranged downstream of the first expansion deviceand configured to receive the first partial stream and to store therefrigerant of the first partial stream in a liquid and gaseous phase.An ejector supply line may be provided for guiding the expanded firstpartial stream in a liquid phase from the separator to the suction inletof the ejector. Prior to being supplied to the ejector, the liquid feedgas stream may be evaporated. In the further development, the coolingsystem may further comprise a closed precooling cycle for precooling therefrigerant stream of the cooling cycle, wherein the closed precoolingcycle has a further refrigerant stream comprising or consisting ofnitrogen, a fourth expansion device for expanding the furtherrefrigerant stream, and a fourth heat exchanger configured to transferheat between the expanded further refrigerant stream and the refrigerantstream and particularly the feed gas stream.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will be more readily appreciated by reference tothe following detailed description when being considered in connectionwith the accompanying drawings in which:

FIG. 1 is a schematic thermodynamic process diagram illustrating anindustrial hydrogen liquefaction plant with a cooling system which usesa cooling method according to an embodiment of the present invention:and

FIG. 2 is a schematic thermodynamic process diagram illustrating afurther industrial hydrogen liquefaction plant with a cooling systemwhich uses the cooling method according to a further embodiment of thepresent invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the following, the invention will be explained in more detail withreference to the accompanying figures. In the figures, like elements aredenoted by identical reference numerals and repeated description thereofmay be omitted in order to avoid redundancies.

FIG. 1 illustrates a process design for an industrial hydrogenliquefaction plant for hydrogen liquefaction on a large-scale. Thedepicted industrial hydrogen liquefaction plant comprises a hydrogencooling and liquefaction unit 10, to which a feed gas stream 12comprising hydrogen is supplied. Upon flowing through the hydrogencooling and liquefaction unit 10, the hydrogen feed gas stream 12 iscooled and thereby liquefied so as to generate a liquid product stream14.

In order to provide cooling energy for cooling and liquefaction of thehydrogen gas stream, the industrial hydrogen liquefaction plant isthermally coupled to a cooling system 16 comprising a precooling cycle18 and a main cooling cycle 20 in form of closed-loop refrigerationcycles. The precooling cycle 18 and the main cooling cycle 20 may beprovided in one or two separate vacuum insulated cold-box vessels. Inthe embodiment shown in FIG. 1, the cooling system comprises aprecooling cold-box 22 and a main cooling cold-box 24.

At first, the main cooling cycle 20 is described in more detail. In themain cooling cycle 20, a refrigerant comprising a cryogenic suitablegas, i. e. hydrogen, circulates, thereby successively passing acompressor unit 26, the precooling cold-box 22 and the main coolingcold-box 24. Prior to entering the precooling cold-box 22, therefrigerant is compressed to high pressure, thereby providing arefrigerant stream 28 flowing through a refrigerant line 30 with apressure typically below 30 bar, e.g. 10 bar, but may also have apressure up to 70 bar or at least 25 bar and particularly with anambient temperature, e.g. 303 K. In general, proper operation may beensured as soon as the refrigerant is compressed to a level allowing forenough enthalpy removal in the further process. In some configurations,this may be achieved at a pressure level of 10 bar. The higher thepressure level of the refrigerant, the higher the heat removal in theturbine, but at the same time, heat exchangers grow in thickness, whichmay affect their efficiency.

Thereafter, the refrigerant stream 28 is guided through the precoolingcold-box 22, where it is precooled to a lower precooling temperature of,e.g. at most 100 K and preferably 80 K. Also, the precooling temperaturemay be 115 K, for example, when the cooling energy for precooling therefrigerant stream 28 is provided by means of a liquid natural gas (LNG)as a cooling fluid. If temperature of the refrigerant is kept above 80 Kand the refrigerant comprises hydrogen, then additional effort may berequired for the purification of the hydrogen prior to entering into thecold-box 24, since impurities may freeze out in the heat exchanger.

Upon flowing through the main cooling cold-box 24, the refrigerantstream 28 is divided into a first partial stream 32 flowing through afirst junction line 34 and a second partial stream 36 flowing through asecond junction line 38. In the first junction line 34, the firstpartial stream 32 is expanded in a first expansion device 40, i.e.through a Joule-Thomson throttle valve, and thereby cooled. In this way,the high pressure first partial stream 32 is processed so as to generatea low pressure expanded first partial stream with a pressureparticularly between 1.1 bar to 8 bar and a temperature sufficiently lowto ensure a proper cooling of the feed gas stream 12, e.g. between 20 Kand 24 K. Thereafter, the expanded first partial stream is supplied to agas liquid separator 44 arranged downstream of the first expansiondevice 40 and configured to store the refrigerant in a liquid andgaseous phase. From the separator 44, a liquid expanded first partialstream 42, i.e. the expanded first partial stream 32 comprising hydrogenin a liquid phase, is guided through a first heat exchanger 46.

Specifically, the first heat exchanger 46 is provided in form of aplate-fin heat exchanger through which both the feed gas stream 12 andthe expanded first partial stream 42 in its liquid phase are guided.Accordingly, the first heat exchanger 46 is configured to transfercooling energy from the expanded first partial stream 42 to the feed gasstream 12 to be cooled. More specifically, cooling energy is transferredfrom the expanded first partial stream 42 to the feed gas stream 12 suchthat the feed gas stream 12 is cooled to a temperature below thecritical temperature of hydrogen, particularly below 24 K, therebyensuring that the liquid product stream 14 is output from the hydrogencooling and liquefaction unit 10. At the same time, heat of reactionfrom the ortho para conversion is removed in preferably every heatexchanger passage of the liquefaction unit 10 following the absorber104. In a further development, the ortho para conversion may beintegrated into the absorber 104.

In the main cooling cycle 20, the cooling system 16 comprises an ejector48 having a propellant inlet and a suction inlet. After passing thefirst heat exchanger 46, the expanded first partial stream 42 is guidedto the suction inlet of the ejector 48. Further, the second partialstream 36, after being partially expanded in a second expansion device50 comprising a throttle valve and an expansion turbine, is guided tothe propellant inlet of the ejector 48. Accordingly, the suction inletof the ejector 48 is connected to the first junction line 34 forreceiving the expanded first partial stream 42 and the propellant inletof the ejector 48 is connected to the second junction line 38 forreceiving a partially expanded second partial stream 52. Additionally,for control purposes, the second partial stream 36 at least partiallymay be guided directly into the ejector 48 by bypassing the secondexpansion device 50. Compared to the expanded first partial stream 42,the partially expanded second partial stream 52 has an intermediatepressure level that is higher than the low-pressure level of theexpanded first partial stream 42.

In this configuration, the ejector 48 functions as a pumping devicewhich is driven by the partially expanded second partial stream 52 andconfigured to compress the expanded first partial stream 42. Morespecifically, the partially expanded second partial stream 52constitutes a propellant medium which, upon flowing through the ejector48 and due to a momentum transfer induced by the geometric configurationof the ejector 48, compresses the expanded first partial stream 42 whichconstitutes a suction medium.

In the following, the configuration and operation of the ejector 48 isdescribed in more detail. The ejector 48 comprises the propellant inletfor receiving the pressurized propellant that is supplied to a nozzle,i.e. a laval nozzle, communicating to a suction chamber of the ejector48. The ejector further comprises the suction inlet which opens into thesuction chamber and is configured to supply the suction fluid into thesuction chamber, wherein the suction fluid has a pressure lower than apressure of the propellant fluid supplied to the propellant inlet. Thesuction chamber communicates to a fluid outlet of the ejector 48 via aconvergent-divergent diffuser.

In operation of the ejector 48, the pressurized propellant fluid, i.e.the partially expanded second partial stream 52 enters the propellantinlet of the ejector 48 and is then accelerated to a high velocitythrough the nozzle which discharges a high velocity jet stream of thefluid through the suction chamber into the convergent-divergentdiffuser. As a result, a reduced pressure in the chamber is generatedcausing a draw in of the expanded first partial stream 42 which isentrained by and drawn into the convergent-divergent diffuser with thehigh velocity fluid stream. The thus combined fluid undergoescompression as it passes through a convergent inlet portion of thediffuser and, thereafter, deceleration and expansion as it passesthrough the divergent outlet portion of the diffuser.

In this way, upon expanding the partially expanded second partial streamin the ejector 48, the expanded first partial stream 42 is compressedand merged with the expanded second partial stream, thereby generatingan expanded refrigerant stream 54 output by the ejector 48 into arecirculation line 56. In this configuration, the ejector 48 is providedsuch that the expanded refrigerant stream 54 output by the ejector 48has a medium pressure level that is higher than the low pressure levelof the expanded first partial stream 42 and lower than the intermediatepressure level of the partially expanded second partial stream 52.

Further, the expanded refrigerant stream 54, the first partial stream 32and the feed gas stream 12 are guided through a second heat exchanger 58such that heat is transferred therebetween. Specifically, the coolingsystem 16 comprises the second heat exchanger 58 in form a plate-finheat exchanger, through which the expanded refrigerant stream 54, thefirst partial stream 32 and the feed gas stream 12 are guided and whichis configured to transfer cooling energy from the expanded refrigerantstream 54 to both the first partial stream 32 and the feed gas stream12.

In the main cooling cycle 20, the refrigerant stream 28 is furtherdivided, at different temperature levels, into a third partial stream 60flowing through a third junction line 62 and a fourth partial stream 64flowing through a fourth at junction line 65. In the third junction line62, a third expansion device 66 is arranged which is configured toexpand the third partial stream 60 so as to generate an expanded thirdpartial stream 68. Specifically, the third expansion device 66comprises, for example, two expansion turbines connected in series inthe third junction line 62. In an alternative embodiment, the thirdexpansion device may also comprise one or more expansion turbinesconnected in series and/or in parallel.

The expanded third partial stream 68 together with the expandedrefrigerant stream 54, the first partial stream 32 together with thesecond partial stream 36, and the feed gas stream 12 are guided througha third heat exchanger 70 such that cooling energy is transferred fromthe expanded refrigerant stream 54 and the expanded first partial stream68 to the first partial stream 32, the second partial stream 36 and thefeed gas stream 12. Specifically, the expanded third gas stream 68 issupplied from the third expansion device 66 via a first supply line 72to the recirculation line 56 downstream of the third heat exchanger 70.In other words, the first supply line 72 is configured to feed theexpanded third partial stream 68 two the expanded refrigerant stream 54downstream of the third heat exchanger 70.

In the fourth junction line 65, a fourth expansion device 74 is arrangedwhich is configured to expand the fourth partial stream 64 so as toprovide an expanded fourth partial stream 76. In an alternativeembodiment, the liquefaction plant 10 may also comprise more or lessthan four junction lines, i.e. depending on the plant capacity.Specifically, the fourth expansion device 74 comprises, for example, twoexpansion turbines connected in series in the fourth junction line 65.Each of the expansion devices 50, 66, 74 is configured for or has thefunction of performing a gas expansion such that mechanical labor isremoved from the respective gas stream. For doing so, the design of eachexpansion device 50, 66, 74 may be adapted to a capacity of the plant10. Thus, of course, the configuration of these components may differcompared to the present design depending on the specific application.For example, each expansion device may comprise one or more expansionturbines or other expansion units which may be arranged in series and/orin parallel.

The expanded fourth partial stream 76, the first partial stream 32, thesecond partial stream 36, the third partial stream 60, the expandedrefrigerant stream 54 and the feed gas stream 12 are guided through afourth heat exchanger 78. The fourth heat exchanger 78 is configured totransfer cooling energy from the expanded fourth partial stream 76, theexpanded third partial stream 68 and the expanded refrigerant stream 54to the first to third partial streams 32, 36, 60 and the feed gas stream12. Specifically, this is realized by supplying the expanded fourthpartial stream 76 via a second supply line 80 from the fourth expansiondevice 74 to the recirculation line 56 downstream of the fourth heatexchanger 78. In other words, the second supply line 80 is configured tofeed the expanded fourth partial stream 76 to the expanded refrigerantstream 54 downstream of the fourth heat exchanger 78.

The recirculation line 56 is configured to guide the expandedrefrigerant stream 54 and the expanded third and fourth partial streams68, 76 to the compressor unit 26. The compressor unit 26 comprises apiston compressor system 82 which is configured to, upon being flownthrough with the fluid stream flowing through the recirculation line 56,compress the expanded refrigerant stream together with the expandedthird and fourth partial streams 68, 76, thereby providing therefrigerant stream 28. In this way, a closed cooling cycle is provided.Specifically, as depicted in FIG. 1, the piston compressor system 82comprises two piston compressors. Alternatively, the piston compressorssystem 82 may comprise one or more piston compressors.

After being compressed by the piston compressors 82, the refrigerantstream 28 is guided through a fifth heat exchanger 84, which is fed witha cooling water stream 86. Specifically, the fifth heat exchanger 84 isconfigured to transfer cooling energy from the cooling water stream 86to the refrigerant stream 28. Downstream of the fifth heat exchanger 84,the cooling water passes through a valve 88.

Upon flowing through the precooling cold-box 22, the refrigerant stream28 is precooled by means of the closed precooling cycle 18 which has afurther refrigerant stream 90 comprising or consisting of nitrogen orliquefied natural gas (LNG). Specifically, the further refrigerantstream 90 is expanded in a fifth expansion device 92 provided in form ofa throttle valve prior to being successively supplied to a further gasliquid separator 94 and a sixth heat exchanger 96. Specifically, thesixth heat exchanger 96 is configured to transfer cooling energy fromthe further refrigerant stream 90 and the fluid flowing through therecirculation line 56 to the refrigerant stream 28 and the feed gasstream 12. By means of the further separator 94, the further refrigerantstream 90 is separated into a mainly gaseous phase and a many liquidphase, wherein the mainly liquid phase is separately guided through thesixth heat exchanger 96. The third to sixth heat exchangers 70, 78, 84and 96 are provided in form plate-fin heat exchangers.

At the outlet of the sixth heat exchanger 96, the refrigerant stream 28is guided through an adsorber 98 to remove impurities present in therefrigerant stream 28. In case the refrigerant stream 28 comprises orconsist of LNG, the adsorber 104 may be located further downstream.Further, at the outlet of the fifth heat exchanger 84, a third supplyline 100 is provided comprising a valve 102, via which gaseousrefrigerant, e. g. hydrogen, for example from a storage tank,particularly a high pressure storage tank and/or a mobile storage tank,can be supplied into the refrigerant line 30.

In the following, the configuration of the hydrogen cooling andliquefaction unit 10 is described in more detail. After entering thehydrogen cooling and liquefaction unit 10, the feed gas stream 12 isguided through the sixth heat exchanger 96 so as to be precooled to alower precooling temperature, e.g. 100 K, particularly by the precoolingcycle 18. At the outlet of the sixth heat exchanger 96, residualimpurities are removed from the precooled hydrogen feed gas 12 by meansof adsorber vessels 104. After this feed gas purification by means ofthe adsorber vessels 104, the precooled feed gas stream 12 is routedback to the sixth heat exchanger 96 through a passage 106 filled with acatalyst. In this way, the precooled feed gas stream 12 is brought intocontact with the catalyst being able to catalyze a conversion of orthohydrogen to para hydrogen. Thereafter, the feed gas stream 12successively passes the fourth, third and second heat exchangers 78, 70,58 having integrated catalyst prior to being supplied to a sixthexpansion device comprising a throttle valve 108 and a further ejector110. After passing the sixth expansion device, the feed gas stream 12 isguided through the first heat exchanger 46 and a seventh expansiondevice 112 so as to generate the liquid product stream 14 having astorage pressure in the range of 1 to 3.5 bar. The thus generated liquidproduct stream 14 is guided to a storage tank configured to storehydrogen in its liquid and gaseous phase.

Specifically, the further ejector 110 has a propellant inlet forreceiving the feed gas stream 12 and a suction inlet for receiving agaseous hydrogen stream 114. Preferably, the gaseous hydrogen stream 114is discharged from the storage tank and supplied to the suction inlet ofthe further ejector 110.

Furthermore, downstream of the adsorber vessels 104, a branch line 116is provided having a throttle valve 118, via which at least a part ofthe feed gas stream 12 can be branched off and supplied to therecirculating line 56 of the main cooling cycle 20.

FIG. 2 depicts a process design for an industrial hydrogen liquefactionplant for hydrogen liquefaction on a large-scale according to a furtherembodiment. The following description of the liquefaction plantparticularly involves the differences compared to the previouslydescribed embodiment depicted in FIG. 1 so as to omit a repeateddescription and to avoid redundancies.

As depicted in FIG. 2, upon flowing through the main cooling cold-box24, the refrigerant stream 28 is divided into the first partial stream32 flowing through the first junction line 34 and the second partialstream 36 flowing through the second junction line 38. Prior to beingbranched off, the refrigerant stream 28 is guided through a seventh heatexchanger 120. The seventh heat exchanger 120 is provided such that thefeed gas stream 12 is guided therethrough upstream of the sixth heatexchanger 96 and downstream of the fourth heat exchanger 78 so as totransfer heat from the feed gas stream 12 to the expanded refrigerantstream 56.

The first partial stream 32, after being branched off from therefrigerant stream 28, is successively guided through the fourth, thethird and the second heat exchanger 78, 70, 58 and thereafter through aneighth heat exchanger 122 prior to being supplied to the separator 44.The eighth heat exchanger 122 is provided such that the feed gas stream12 is guided therethrough upstream of the second heat exchanger 58 anddownstream of the further ejector 110 so as to transfer heat from thefeed gas stream 12 to the expanded refrigerant stream 56.

The second partial stream 36, after being partially expanded in a secondexpansion device 50, is guided through the third heat exchanger 70 andthereafter to the propellant inlet of the ejector 48. In a furtherdevelopment, for control purposes, the second partial stream 36 at leastpartially may be guided directly into the ejector 48 and/or the thirdheat exchanger 70 by bypassing the second expansion device 50.

Further, separate to a first suction line for supplying the liquidexpanded first partial stream 42 from the separator 44 to the suctioninlet of the ejector 48, a second suction line 124 is provided forsupplying a gaseous expanded first partial stream 126, i.e. a part ofthe expanded first partial stream 32 comprising hydrogen in a gaseousphase, from the separator 44 to a further suction inlet of the ejector48. Compared to the liquid expanded first partial stream 42, the gaseousexpanded first partial stream 126 bypasses the first heat exchanger 46.The second suction line may also be provided in the configurationdepicted in FIG. 1.

Upstream of the further ejector 110 and downstream of the first heatexchanger 46, a further branch line 128 is provided having a throttlevalve 130, via which at least a part of the feed gas stream 12 can bebranched off and supplied to the separator 44.

It will be obvious for a person skilled in the art that theseembodiments and items only depict examples of a plurality ofpossibilities. Hence, the embodiments shown here should not beunderstood to form a limitation of these features and configurations.Any possible combination and configuration of the described features canbe chosen according to the scope of the invention.

LIST OF REFERENCE NUMERALS

10 hydrogen cooling liquefaction unit

12 feed gas stream

14 liquid product stream

16 cooling system

18 precooling cycle

20 main cooling cycle

22 precooling cold-box

24 main cooling cold-box

26 compressor unit

28 refrigerant stream

30 refrigerant line

32 first partial stream

34 first junction line

36 second partial stream

38 second junction line

40 first expansion device

42 liquid expanded first partial stream

44 gas liquid separator

46 first heat exchanger

48 ejector

50 second expansion device

52 partially expanded second partial stream

54 expanded refrigerant stream

56 recirculation line

58 second heat exchanger

60 third partial stream

62 third junction line

64 fourth partial stream

65 fourth junction line

66 third expansion device

68 expanded third partial stream

70 third heat exchanger

72 first supply line

74 second expansion device

76 expanded fourth partial stream

78 fourth heat exchanger

80 second supply line

82 piston compressor system

84 fifth heat exchanger

86 cooling water stream

88 throttle valve

90 further refrigerant stream

92 throttle valve

94 further gas liquid separator

96 sixth heat exchanger

98 adsorber

100 third supply line

102 throttle valve

104 adsorber vessel

106 heat exchanger passage

108 throttle valve

110 further ejector

112 seventh expansion device

114 gaseous hydrogen stream

116 branch line

118 throttle valve

120 seventh heat exchanger

122 eighth heat exchanger

124 second suction line

126 gaseous expanded first partial stream

128 further branch line

130 further throttle valve

1. Cooling method for liquefying a feed gas, comprising the steps of:providing a cooling cycle with a refrigerant stream; dividing therefrigerant stream into a first partial stream and a second partialstream; expanding the first partial stream in a first expansion device;and, transferring cooling energy from the expanded first partial streamto a feed gas stream to be cooled, wherein the method further comprisesthe steps of: guiding the expanded first partial stream to a suctioninlet of an ejector; and, guiding the second partial stream to apropellant inlet of the ejector such that, upon expanding the secondpartial stream in the ejector, the expanded first partial stream iscompressed and merged with the expanded second partial stream.
 2. Methodaccording to claim 1, wherein, by transferring cooling energy from theexpanded first partial stream to the feed gas stream to be cooled,particularly by means of a first heat exchanger, the feed gas stream iscooled to a temperature below the critical temperature of hydrogen,particularly below 24 K, so as to provide a liquid product streamcomprising hydrogen.
 3. Method according to claim 1, wherein an expandedrefrigerant stream is provided by merging the compressed first partialstream with the expanded second partial stream in the ejector, andwherein the method further comprises the step of guiding the expandedrefrigerant stream through a compressor unit, particularly comprising orconsisting of at least one piston compressor so as to compress theexpanded refrigerant stream, thereby providing the refrigerant stream.4. Method according to claim 1, further comprising the step of guidingthe expanded refrigerant stream and the first partial stream such thatheat is transferred, particularly by means of a second heat exchanger,between the expanded refrigerant stream and the first partial stream andparticularly the feed gas stream.
 5. Method according to claim 1,further comprising the step of partially expanding the second partialstream in a second expansion device particularly a Joule-Thomson-valveand/or an expansion turbine, prior to being guided to the ejector and/orthe step of guiding the second partial stream) into the ejector,particularly by bypassing the second expansion device.
 6. Methodaccording to claim 1, wherein the refrigerant stream is furtherseparated into at least one third partial stream, particularly atdifferent temperature levels, and the method further comprises the stepsof: expanding the at least one third partial stream in at least onethird expansion device, particularly in at least one expansion turbine;and guiding the at least one expanded third partial stream and the firstpartial stream such that heat is transferred, particularly by means ofat least one third heat exchanger, between the at least one expandedthird partial stream and the first partial stream and particularly thefeed gas stream; and, feeding the at least one expanded third partialstream to the expanded refrigerant stream.
 7. Method according to claim1, wherein the expanded first partial stream is guided into a gas liquidseparator arranged downstream of the first expansion device andconfigured to store the refrigerant in a liquid and gaseous phase, andwherein the expanded first partial stream in a liquid phase is guidedfrom the separator, particularly through the first heat exchanger actingas an evaporator, to the suction inlet of the ejector.
 8. Methodaccording to claim 1, wherein the refrigerant stream) is precooled bymeans of a closed precooling cycle having a further refrigerant streamcomprising or consisting of nitrogen, wherein in particular the furtherrefrigerant stream is expanded in a fourth expansion device prior tobeing supplied to a fourth heat exchanger for transferring coolingenergy to the refrigerant stream and particularly to the feed gasstream.
 9. Cooling system for liquefying a feed gas, having a coolingcircuit with a refrigerant line for circulating a refrigerant stream,wherein the cooling circuit further comprises: an expansion deviceconfigured to expand a first partial stream flowing through a firstjunction line branching off from the refrigerant line; and, a heatexchanger for transferring cooling energy from the expanded firstpartial stream to a feed gas stream to be cooled, wherein the coolingcircuit further comprises an ejector having a suction inlet connected tothe first junction line for receiving the expanded first partial streamand a propellant inlet connected to a second junction line branching offfrom the refrigerant line for receiving a second partial stream, whereinthe ejector is configured to, upon expanding the second partial streamin the ejector, compress the expanded first partial stream and merge itwith the expanded second partial stream.
 10. Cooling system according toclaim 9, wherein the heat exchanger is configured to transfer coolingenergy from the expanded first partial stream to the feed gas stream tobe cooled such that the feed gas stream is cooled to a temperature belowthe critical temperature of hydrogen, particularly below 24 K, so as toprovide a liquid product stream comprising hydrogen.
 11. Cooling systemaccording to claim 9, wherein the cooling system further comprises acompressor unit configured to compress an expanded refrigerant streamoutput by the ejector and formed by merging the compressed first partialstream with the expanded second partial stream so as to provide therefrigerant stream, and wherein the compressor unit comprises orconsists of at least one piston compressor.
 12. Cooling system accordingto claim 9, further comprising a second heat exchanger configured totransfer heat between the expanded refrigerant stream and the firstpartial stream and particularly the feed gas stream.
 13. Cooling systemaccording to claim 9, further comprising a second expansion device,particularly a Joule-Thomson-valve and/or an expansion turbine, arrangedupstream of the ejector and configured to partially expand the secondpartial stream flowing through the second junction line, whereinparticularly a bypass line is provided through which at least a part ofthe second partial stream is guided and which is configured forbypassing the second expansion device and guiding the second partialstream flowing therethrough into the ejector.
 14. Cooling systemaccording to claim 9, further comprising: at least one third expansiondevice configured to expand at least one third partial stream flowingthrough at least one third junction line which branches off from therefrigerant line at different temperature levels, at least one thirdheat exchanger for transferring heat between the at least one expandedthird partial stream and the first partial stream and particularly thefeed gas stream; and, at least one supply line arranged downstream ofthe at least one third heat exchanger for feeding the at least oneexpanded third partial stream to the expanded refrigerant stream. 15.Cooling system according to claim 9, further comprising: a gas liquidseparator arranged downstream of the first expansion device andconfigured to receive the expanded first partial stream and to store therefrigerant of the expanded first partial stream in a liquid and gaseousphase, an ejector supply line for guiding the expanded first partialstream in a liquid phase from the separator, particularly evaporated inthe first heat exchanger, to the suction inlet of the ejector, and/or aclosed precooling cycle for precooling the refrigerant stream of thecooling cycle, wherein the closed precooling cycle has a furtherrefrigerant stream, particularly comprising or consisting of nitrogen orliquid natural gas, a fourth expansion device for expanding the furtherrefrigerant stream, and a fourth heat exchanger configured to transferheat between the expanded further refrigerant stream and the refrigerantstream and particularly the feed gas stream.